The objectives of this project are to better define growth control mechanisms in nontransformed cells and the alterations which occur in chemically transformed cells. Based in large part on studies performed in this project, the following hypothesis has been developed. Nontransformed cells have at least two separate and distinct G1 arrest points-a growth factor deficiency arrest point occurring early in G1 (G0 arrest) and a low molecular weight nutrient deficiency arrest point occurring later in G1. Chemically transformed cells arrest growth in G1 only at the latter nutrient arrest point. G0 arrested nontransformed cells have low levels of RNA metabolism, and following stimulation, there is an early growth factor dependent stage involving transcription of structural genes and new ribosome synthesis while a later stage in late G1 requiring low molecular weight nutrients is dependent upon insulin or insulin-like hormones. Cells in the nutrient arrest state have higher levels of RNA content and metabolism and need only to achieve the latter step to enter the S phase. To further test this hypothesis growth factor deficiency arrested nontransformed cells will be characterized with respect to sequential growth factor, hormonal, and nutrient requirements with a determination of growth arrest points between G0 and S. Studies on general ribosomal and messenger RNA metabolism will be performed at the different arrest points and following stimulation. To study specific gene expression in association with cell proliferation and chemical transformation, mouse genomic libraries will be screened to identify clones expressed only in stimulated or G0 arrested nontransformed cells. After preliminary characterization, these clones will be used to examine gene expression at the different arrest points and to identify gene sequences whose expression is dependent upon growth factor and/or hormonal stimulation of cell proliferation.